1. Field of the Invention
The present invention typically relates to, in a motorcycle in which an engine is mounted on vehicle body frames extended diagonally rear downward from a steering head pipe, a structure of an air cleaner disposed above the engine.
2. Description of the Related Art
Generally, as a method of improving aerodynamic characteristics (Coefficient of Drag CD×frontal projected area A) of a vehicle such as a motorcycle, it is effective to narrow a width of vehicle body frames to make elbows and knees of a passenger or a rider to be positioned inwardly. Particularly, in a vehicle in which an engine with wide width in right and left directions such as a parallel multicylinder engine is mounted, a width of vehicle body frames is increased, if no measure is taken. Especially in a case where it is structured such that an air cleaner mounted above an engine is detached/attached from a position above vehicle body frames, an opening of an upper part of the vehicle body frames is required to have a size equal to or larger than a size of the air cleaner, resulting in that a width is increased. Accordingly, since it is not possible to make elbows and knees of a rider to be positioned toward the inside of the vehicle, a frontal projected area is increased, and an aerodynamic performance is lowered. Further, since a degree of freedom when a rider rides the vehicle is also lowered, a degree of fatigue at a time of driving for a long period of time becomes large.
For example, in a motorcycle disclosed in Patent Document 1, a technique for improving an aerodynamic performance and enlarging a degree of freedom when a rider rides the motorcycle is disclosed. In this example, a width of vehicle body frames is reduced by adopting a monocoque frame integrated with an air cleaner box.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2007-76553.
The monocoque frame such as one in Patent Document 1 is a unit effective for manufacturing a compact vehicle, but, it has a structure with which a control of rigidity of the vehicle body frames is difficult. Meanwhile, in a vehicle required to have a high-speed performance such as a racer, a conventional twin spar frame excellent in high rigidity is the most suitable. However, when a parallel multicylinder engine is mounted on the twin spar frame, practically it cannot be said that a structure in which an air cleaner is attached/detached from a position above the vehicle body frames is suitable for aerodynamic characteristics and the like, if no measure is taken.